Various intermediate products and raw materials produced in non-ferrous metal smelting or refining processes contain unfavorable elements, such as arsenic, although they contain valuable metals.
As a conventional method for leaching, separating and recovering arsenic from arsenic containing intermediate products in smelting or refining processes, there has been proposed a method for separating arsenic from an arsenic containing intermediate product by a wet reaction to recover an arsenic containing solution (see, e.g., Japanese Patent Publication No. 61-24329). There is also proposed a method for removing and fixing arsenic, which exists in an iron arsenate solution, as a stable crystalline compound of iron and arsenic, which does not elute or release metals (see, e.g., Japanese Patent Laid-Open No. 11-277075). In addition, there is proposed a method for adding at least one of an iron (II) solution and an iron (III) solution to an arsenic containing solution to allow a reaction to form Scorodite (FeAsO4.2H2O) to carry out a solid-liquid separation to recover the Scorodite, which contains non-ferrous metals including copper, to add water to the obtained Scorodite, which contains the non-ferrous metals including copper, to carry out repulping to dissolve the non-ferrous metals including copper, which are contained in the Scorodite, in the solution to separate the non-ferrous metals including copper from the Scorodite (see, e.g., Japanese Patent Laid-Open No. 2000-219920). Moreover, there is proposed a method for leaching arsenic from an arsenic containing flue cinder with an acid solution to mix the leached arsenic containing solution with an aqueous acidic solution containing iron ions to precipitate amorphous ferric arsenate (FeAsO4) to heat the mixed solution to crystallize the amorphous ferric arsenate to filter the mixed solution to remove the crystallized ferric arsenate (see, e.g., Japanese Patent Laid-Open No. 2005-161123).
Japanese Patent Publication No. 61-24329 has proposed the method for recovering an arsenic containing solution, but it does not propose a method for fixing the recovered arsenic containing solution as a stable substance which does not elute metals. In addition, it is desired to form a compound of iron and arsenic which is more stable and is more difficult to elute metals than conventional compounds of iron and arsenic produced by the methods proposed in Japanese Patent Laid-Open Nos. 11-277075, 2000-219920 and 2005-161123. Particularly, there is a problem in that it takes a lot of time to carry out the method proposed in Japanese Patent Laid-Open No. 2005-161123, since amorphous iron arsenate is crystallized after the amorphous iron arsenate is precipitated.